retrohax.net

… or GEL PENS to the rescue

Intro

/Intro

Ok, today I am writing about the Atari 1020 plotter. This is one of many plotters that use the ALPS plotting mechanism. I have at least one more plotter for VIC-20 that is very similar to this one. This is all done for one of my clients – Cheers W :>

The story of this particular unit is simple. My client asked me to get such an Atari plotter so he can start playing with it. I’ve posted a buying request on the great AtariArea community forums and surely get a response! Jer, who is a great guy and a respected member of the Atari community, replied to me and offered this particular 1020 plotter. We’ve made a deal and the plotter landed in my garage. It had to wait at least 2 years on the shelf until I picked it up …. yeah, the queue is long and the days are too short.

Enough of moaning, let’s do some work.

Cleaning, disassembly, and testing

The unit was in a VERY good shape so I didn’t have to spend days cleaning and retr0brighting it.

I only had to de-dust it and clean the rollers and that’s it.

Here is how it looked.

Dry run of the semi-assembled unit.

I’ve assembled it all and added some new rubber feet.

The pens

This is where we approach the clue of this blog post – the plotter pens!

Here is a pic of the original pens.

These dudes dried out ages ago and currently are useless. Yes, I’ve tried refilling ’em but that was kind of a failure. Even after ultrasonic cleaning in IPA solution and refilling with fresh ink, the original pens just didn’t work 🙁

However, we have 3D printers nowadays so why not make new ones!?

One evening I was having a coffee and I looked at the table and I was like …

I’ve spotted a multi-color ball pen on the kitchen table! I was like hell yeah! this might work.

It is a standard 4-color ball pen with colors that are needed for this plotter – red, green, blue, and black – exactly what we need!!

I did some measurements, designed a new cartridge case and 3D printed it out of UV resin.

The idea was to use a cut to a proper size ball pen refill and insert it into a freshly 3D printed case.

Here is how it looked.

The standard refill insert is 3mm in diameter and fits perfectly into a 3D-printed case.

I’ve fired up an AtariWriter+ software and run some tests!

Unfortunately, it didn’t work at all 🙁

Turns out that the pressure on the pen itself is too weak. We need to dive deeper!

The hunt for a proper pen pressure

This is where I started to analyze the mechanism a bit deeper.

In the following pic, you can see a carriage with an anti-spring in the form of a steel rosette which helps to keep a drawing pen away when it moves freely.

Here is another important piece – the electromagnet that drives a bar that in turn drives a hammer.

Now, my diagnosis was that the hammer bar was not putting enough pressure to start my replacement cartridge drawing. This pressure is controlled by a spring that is located on the other end of the hammer bar.

My idea was to make another turn of that spring. That was harder to do than I thought (yup, lots of tries with pincers of various types failed) but after some time, I came up with an idea to pull it with a piece of looped wire!

I’ve made a loop on the end of the copper wire and used it to pull the spring downside to catch it with pliers and bring it up again! SUCCESS…. but still not enough…

After spring tuning, the results were better but still crappy so I had to think about something else.

Gel pens to the rescue!

I am not much into the pens industry but I know that gel pens need less pressure to write.

I’ve ordered some different brands of gel pens and waited for delivery. Meanwhile, I was discussing these issues on the AtariArea Discord channel and one of the users (cheers Perinoid!) suggested using Gel pens too!!! Great minds think alike!

A while later I was ready to run some more tests!

I had to cut the gel refill inserts first as usual. The measuring procedure is simple. You just have to measure the length of the original cartridge and then cut the refill insert to a size, minus 2mm. This is because the pointy end of the case is exactly 2mm long.

Here is a comparison of all three pens.

Some test results

For the final test, I’ve rewritten a few lines of code that I’ve found in this article

Here is how this code works.

Results:

Here is the final look of the pens with original covers.

The next plotter in the queue is VIC 1520 – Printer Plotter :>

Downloads

Atari 1020 field service manual

AtariWriter+ ATR

Models for 3D Printing

Outro

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